1.8L L4 VIN 8 Auto 7

The scan tool output control feature, Fuel Injector Modification, can be used at idle to check the oxygen sensor performance. Commanding the Fuel Injector Modification Commanded State to 25 percent should cause the HO2S 1 voltage to decrease to less than 3 volts. Changing the Fuel Injector Modification Commanded State to -12 percent should cause the HO2S 1 voltage to increase to more than 3.35 volts. An oxygen sensor that fails to respond accordingly may be faulty or contaminated. When performing the Fuel Injector Modification with the scan tool, the Loop Status will remain Open Loop and the Short Term FT will be fixed at 0 percent.

Inspect for a contaminated HO2S. Silicon contamination of the HO2S can cause a low signal voltage to be indicated. Silicon contamination is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. Before replacing the HO2S determine the cause of the contamination and correct the condition.

Verify the PCM to engine electrical grounds are OK.

An incorrect fuel pressure--The fuel system can go lean if the fuel pressure is too low and DTC P2A00 can be set. Refer to Fuel System Diagnosis .

Fuel contamination--Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Any vacuum leaks--Inspect for disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, the throttle body, and the crankcase ventilation system.

Any exhaust leaks near the HO2S--An exhaust leak may cause outside air to be pulled into the exhaust gas stream and past the HO2S causing DTC P2A00 to set.

An intermittent malfunction may be caused by fault in the HO2S 1 electrical circuit. Inspect the wiring harness and components for any intermittent conditions. Refer to Intermittent Conditions .

Trouble Code: U0073

CAN Bus Communication

Possible Causes:

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and the connectors may result in a misdiagnosis, causing a part replacement with the reappearance of the malfunction. The following are possible causes of the malfunction:

An open or high resistance in the CAN - high or CAN - low circuits

A short between the CAN - high and CAN - low circuits

A short to ground in the CAN - high or CAN - low circuits

A short to voltage in the CAN - high or CAN - low circuits

A steering wheel position sensor malfunction

A yaw rate sensor malfunction

An internal EBCM malfunction

Trouble Code: U0073

CAN Bus Communication

Possible Causes:

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and the connectors may result in a misdiagnosis, causing a part replacement with the reappearance of the malfunction. The following are possible causes of the malfunction:

An open or high resistance in the CAN - high or CAN - low circuits

A short between the CAN - high and CAN - low circuits

A short to ground in the CAN - high or CAN - low circuits

A short to voltage in the CAN - high or CAN - low circuits

A steering wheel position sensor malfunction

A yaw rate sensor malfunction

An internal EBCM malfunction

Trouble Code: U0123

Yaw Rate Circuit Malfunction

Possible Causes:

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and the connectors may result in a misdiagnosis, causing a part replacement with the reappearance of the malfunction. The following are possible causes of the malfunction:

An open or high resistance in the yaw rate sensor ground circuit

An open, high resistance, or short to ground in the yaw rate sensor ignition voltage circuit

A yaw rate sensor malfunction

Trouble Code: U0124

CAN Bus Communication

Possible Causes:

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and the connectors may result in a misdiagnosis, causing a part replacement with the reappearance of the malfunction. The following are possible causes of the malfunction:

An open or high resistance in the yaw rate sensor ground circuit

An open, high resistance, or short to ground in the yaw rate sensor ignition voltage circuit

A yaw rate sensor malfunction

Trouble Code: U0126

CAN Steering Position Sensor Circuit Malfunction

Possible Causes:

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and the connectors may result in a misdiagnosis, causing a part replacement with the reappearance of the malfunction. The following are possible causes of the malfunction:

An open or high resistance in the steering wheel position sensor ground circuit

An open, high resistance, or short to ground in the steering wheel position sensor ignition voltage

A steering wheel position sensor malfunction

Trouble Code: U0126

CAN Steering Position Sensor Circuit Malfunction

Possible Causes:

Thoroughly inspect the wiring and the connectors. An incomplete inspection of the wiring and the connectors may result in a misdiagnosis, causing a part replacement with the reappearance of the malfunction. The following are possible causes of the malfunction:

An open or high resistance in the steering wheel position sensor ground circuit

An open, high resistance, or short to ground in the steering wheel position sensor ignition voltage

A steering wheel position sensor malfunction

Trouble Code: U1001

Lost Communication With XXX Module

Trouble Code: U1254

Lost Communication with XXX

Trouble Code: U1300

Class 2 Data Link Low

Possible Causes:

These DTCs cannot be retrieved with a current status. Diagnosis of current DTCs is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to Scan Tool Does Not Communicate with Class 2 Device .

An intermittent condition is likely to be caused by a short on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to Scan Tool Does Not Communicate with Class 2 Device .

Trouble Code: U1301

Class 2 Data Link High

Possible Causes:

These DTCs cannot be retrieved with a current status. Diagnosis of current DTCs is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to Scan Tool Does Not Communicate with Class 2 Device .

An intermittent condition is likely to be caused by a short on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to Scan Tool Does Not Communicate with Class 2 Device .

Trouble Code: U1305

Class 2 Data Link Performance

Possible Causes:

These DTCs cannot be retrieved with a current status. Diagnosis of current DTCs is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to Scan Tool Does Not Communicate with Class 2 Device .

An intermittent condition is likely to be caused by a short on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to Scan Tool Does Not Communicate with Class 2 Device .

Trouble Code: U1500

Internal Comunication Malfunction

Possible Causes:

The diagnostic procedure used for DTC U1500 in OnStar® systems with single module generations of OnStar® differ greatly from previous generations with 2 modules. While these older generations denoted a failure of the 3-wire bus between the modules by setting a U1500, single module OnStar® systems use this DTC to denote an internal module failure. The determination of whether a one or 2-module generation of OnStar® is used should be confirmed. Refer to OnStar Description and Operation .

This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the VCIM.

If this DTC is retrieved as both a current and history DTC, replace the VCIM.

Trouble Code: U1500

Inter-Device Dedicated Bus

Possible Causes:

The diagnostic procedure used for DTC U1500 in OnStar® systems with single module generations of OnStar® differ greatly from previous generations with 2 modules. While these older generations denoted a failure of the 3-wire bus between the modules by setting a U1500, single module OnStar® systems use this DTC to denote an internal module failure. The determination of whether a one or 2-module generation of OnStar® is used should be confirmed. Refer to OnStar Description and Operation .

This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the VCIM.

If this DTC is retrieved as both a current and history DTC, replace the VCIM.